Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

T₁ / (T₂ - T₁)

T₂/ (T₂ - T₁)

(T₁ - T₂)/T₁

(T₂ - T₁)/T₁

2. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 1

1: 3

1: 9

9: 1

3. Freon group of refrigerants are

Non-inflammable and toxic

Nontoxic and non-inflammable

Inflammable

Toxic

4. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Involves no change in volume

Takes place at constant temperature

Takes place at constant pressure

Takes place at constant entropy

5. A bootstrap air cooling system has

One heat exchanger

Three heat exchangers

Four heat exchangers

Two heat exchangers

6. Which of the following cycles uses air as the refrigerant?

Stirling

Bell Coleman

Carnot

Ericson

7. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Brine

Ammonia

Freon

Carbon dioxide

8. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

Normal cooling

Super-cooling

None of these

Sub-cooling or under-cooling

9. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Collect liquid refrigerant and prevent it from going to compressor

Collect vapours

Detect liquid in vapour

Superheat the vapour

10. The minimum temperature to which water can be cooled in a cooling tower is

Dry bulb temperature of air

Ambient air temperature

Dew point temperature of air

Wet bulb temperature of air

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11. The freezing point of sulphur dioxide is

-56.6°C

-135.8°C

-77.7°C

-75.2°C

12. The capillary tube, as an expansion device, is used in

Water coolers

Room air conditioners

Domestic refrigerators

All of these

13. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Unpredictable

Less

Equally

14. Rating of a domestic refrigerator is of the order of

10 tons

0.1 ton

5 tons

40 tons

15. Most thermostatic expansion valves are set for a superheat of

20°C

10°C

5°C

15°C

16. In a lithium bromide absorption refrigeration system

Water is used as a refrigerant and lithium bromide as an absorbent

None of these

Ammonia is used as a refrigerant and lithium bromide as an absorbent

Lithium bromide is used as a refrigerant and water as an absorbent

17. Highest temperature encountered in refrigeration cycle should be

Above critical temperature

Much below critical temperature

At critical Temperature

Near critical temperature of refrigerant

18. The bank of tubes at the back of domestic refrigerator is

Condenser tubes

Refrigerant cooling tubes

Capillary tubes

Evaporator tubes

19. The operating pressure for refrigerating units using R-12 as a refrigerant is

30 bar

2 bar

15 bar

8 bar

20. The boiling point of ammonia is

-33.3°C

-77.7°C

-10.5°C

-30°C

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21. The vapour compression refrigerator employs the following cycle

Reversed Rankine

Reversed Carnot

Carnot

Rankine

22. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

Positive

Negative

Zero

None of these

23. The value of C.O.P in vapour compression cycle is usually

Any one of the above

Always less than unity

Equal to unity

Always more than unity

24. Which of the following statement is correct?

(B) The increase in air movement increases the evaporation from the human body.

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

(D) Both (A) and (B)

25. A thermostatic expansion valve in a refrigeration system

Ensures the evaporator completely filled with refrigerant of the load

Is suitable only for constant load systems

Maintains different temperatures in evaporator in proportion to load

None of the above

26. The curved lines on a psychrometric chart indicates

Dew point temperature

Relative humidity

Dry bulb temperature

Wet bulb temperature

27. The condition of refrigerant after passing through the condenser in a vapour compression system is

Saturated liquid

Dry saturated vapour

Superheated vapour

Wet vapour

28. In a refrigeration system, the expansion device is connected between the

Compressor and condenser

Receiver and evaporator

Evaporator and compressor

Condenser and receiver

29. In a refrigeration system, heat absorbed in comparison to heat rejected is

More for small capacity and less for high capacity

Less

Same

30. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.376

0.6

0.4

0.67

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31. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

32. For obtaining high COP, the pressure range of compressor should be

Any value

Optimum

High

Low

33. Which of the following is not a desirable property of a refrigerant?

Large latent heat

High risibility with oil

Good electrical conductor

Low boiling point

34. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

1.2

0.2

35. The domestic refrigerator uses following type of compressor

Centrifugal

Axial

Miniature sealed unit

Piston type reciprocating

36. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(A) Heat dissipated to the surroundings

(B) Heat stored in the human body

(D) Difference of (A) and (B)

37. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

2.33

3.33

1.33

4.33

38. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

5.12

1.25

2.15

39. Critical temperature is the temperature above which

A gas will never liquefy

A gas will immediately liquefy

Water will never evaporate

Water will evaporate

40. Cooling water is required for following equipment in ammonia absorption plant

Condenser, absorber and separator (rectifier)

Condenser

Absorber

Evaporator

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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